The process for oxidizing olefins by contacting the olefins together with an oxidizing agent with multi-component catalysts is known. Grasselli and Hardman, in U.S. Pat. No. 3,642,930 disclose that certain complex catalysts based on iron, bismuth and molybdenum can be employed in the oxidation of olefins to obtain unsaturated aldehydes and acids. Also, see U.S. Pat. No. 4,001,317 and commonly assigned application Ser. No. 717,838, filed Aug. 26, 1976, now abandoned, the disclosure of which is incorporated herein by reference. Also see British Pat. No. 1,437,235, which discloses catalysts based on oxides of bismuth and molybdenum, which further contain at least one of indium, gallium, lanthanum and aluminum.
The catalysts described in these patents and applications are indeed very desirable for the oxidation of olefins to unsaturated aldehydes and acids. Unfortunately, some of these catalysts exhibit a less than desired redox stability when subjected to stressful conditions. More specifically, it occasionally happens in a commercial facility that the amount of oxygen fed to the reactor along with the olefin feed is either much greater or much less than the desired value. When this happens, it has been found that the catalysts may exhibit a significant decrease in catalytic activity. This, of course, is very disadvantageous.
Accordingly, it is an object of the present invention to provide a new process for the catalytic oxidation of olefins to unsaturated aldehydes and acids which employs catalysts having high redox stability so that the catalysts can withstand major deviations in redox conditions without significant decrease in catalytic activity.